/*=====================================================================*
 *                   Copyright (C) 2011 Paul Mineiro                   *
 * All rights reserved.                                                *
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 * Redistribution and use in source and binary forms, with             *
 * or without modification, are permitted provided that the            *
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 *     above copyright notice, this list of conditions and             *
 *     the following disclaimer.                                       *
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 *     * Redistributions in binary form must reproduce the             *
 *     above copyright notice, this list of conditions and             *
 *     the following disclaimer in the documentation and/or            *
 *     other materials provided with the distribution.                 *
 *                                                                     *
 *     * Neither the name of Paul Mineiro nor the names                *
 *     of other contributors may be used to endorse or promote         *
 *     products derived from this software without specific            *
 *     prior written permission.                                       *
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND              *
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,         *
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES               *
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 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER               *
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 * Contact: Paul Mineiro <paul@mineiro.com>                            *
 *=====================================================================*/

#ifndef __DISTRIBUTION_HH__
#define __DISTRIBUTION_HH__

#include <cmath>

namespace playerpiano
{
  class NormalDistribution
    {
      private:
        static const float halflogtwopi = 0.91893853320467274178;

        float mean;
        float inv_sq_stddev;
        float log_stddev;

        static inline float 
        square (float x)
          {
            return x * x;
          }

      public:
        NormalDistribution (float _mean,
                            float _stddev) 
          : mean (_mean),
            inv_sq_stddev (1.0 / square (_stddev)),
            log_stddev (log (fabs (_stddev)))
          {
          }

        float
        logpdf (float x) const
          {
            return - 0.5 * square (x - mean) * inv_sq_stddev 
                   - halflogtwopi 
                   - log_stddev;
          }

        float
        dlogpdf (float x) const
          {
            return (mean - x) * inv_sq_stddev;
          }

        float
        ddlogpdf (float) const
          {
            return -inv_sq_stddev;
          }
    };
}

#endif // __DISTRIBUTION_HH__
